Blower construction



July 8, 1958 w, s 2,842,307

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United States Patent O ce 284L307 Patented July 8, 1958 exceedingly important feature, particularly in a kitchen installation where the blower parts become loaded, from 2,842,307 time to time, with an accumulation of greasy dirt-the BLOWER CONSTRUCTION Walter A: Spear, Cincinnati, Ohio, assignor to NuTone, Inc., Cincinnati, Ohio, a corporation of New York Original application August 3, 1954, Serial No. 447,586. and this application June 24, 1955, Serial No.

8 Claims. (Cl. 230-117) This invention relates to blowers of the type exemplified by U. S. Patent No. 2,349,668. This type of blower is one which is adapted to be recessed in a ceiling, or in a. wall, or in cabinet structure, to exhaust air from a room, such as a kitchen, and deliver it to the outside atmosphere through a duct which may be enclosed within the walls or ceiling of the building structure. The present application is a division of Serial No. 447,586, filed August 3, 1954.

More specifically, the present invention is directed to improvements in the construction of a blower of the type set forth, which improvements greatly simplify installation and maintenance.

One of the problems which arise in making a blower installation, particularly in an old building structure, is to arrange the duct so that it follows as straight a path as possible from the place of installation to an exhaust outlet. Turns in the duct not only increase the cost of the installation, because of the special fittings required, but they also reduce substantially the efiiciency of the blower due to the increase in resistance to the flow of air through a tortuous duct. Therefore, to be commercially practical, and to avoid the use of special fittings, a blower must be adaptable for connection to an exhaust duct which may lead from the point of installation in any one of a number of different directions. With this in mind, it is one of the objectives of the invention to provide a blower construction which may be altered in a matter of minutes and without the use of special tools to change the exhaust and intake sides thereof as demanded by different installation conditions.

In the preferred embodiment of the invention, I provide a casing to house the blower which has two fixed end walls and two fixed side walls which are permanently joined to one another. One of the fixed side walls has a duct fitting or connector secured thereto. The other two sides of the casing are each adapted to receive a transposable side wall or a shiftable air intake grill. By changing the relative positions of the shiftable grill and the transposable side wall it is found that the blower casing can be made to accommodate substantially all duct conditions likely to be found in ordinary building structures. The simple expedient of inter-changing the positions of the transposable side wall and the intake grill makes it possible to have horizontal intake and discharge, vertical intake and discharge, horizontal intake with vertical discharge, and vertical intake with horizontal discharge. These arrangements of the intake and discharge sides of the blower will accommodate duct work leading from the place of installation at any one of the four sides thereof or leading from it in direct alignment with the opening into the blower recess whether the opening be in a ceiling, or in a wall, or whether it is built into cabinet structure.

Another objective of the invention is to provide a blower construction of the type set forth which may be disassembled easily and quickly by an unskilled person for cleaning purposes without the use of tools. This is an result of air which is laden with cooking greases, along with the usual dust, passing through the blower; The blower wheels which move the air, the electric motor which drives the blower wheels, and volute housings provided to enclose the blower wheels in the present construction are adapted to be removed from the casing through the intake grill side thereof as a unit. This is possible irregardless of the position of the blower casing within a recess. Furthermore, novel means is provided to latch the blower unit in position within the casing so that it is properly aligned with the duct connector irregardless of the position of the casing within a recess. Otherwise expressed, the blower and motor unit may be removed and replaced, latched and -unlatched from the grill side of the casing, which side may be the one opposite to the duct connector or one adjacent to it because of the shiftable nature of the grill. In the preferred embodiment the latch comprises a bail shaped, element which is disposed at 45 -tothe sides of the casing. In this angular relationship it is adapted to function as effectively in either one of the two positions of the grill.

In addition, novel means are provided for removably fastening the volute blower wheel housings to the blower unit so that they may be removed for cleaning. This too is an exceedingly important feature because mostv of the dirt which accumulates inside of a blower is foundon the inside of the blower wheel housings.

A further objective of the invention is to provide novel means to mount the shiftable grill so that. it may be changed from one side of the casingv tothe other without removing it from the casing. Furthermore, the means provided are arranged so that the grill may be swung down and removed from the casing in an installation tov provide adequate room for disengaging and removing the blower unit. This is made possible by means of anovel, pivotable mount which operates in conjunction with one or more coil. springs to provide a toggle action which: is effective in both positions of the grill to hold. the grill in tightly closed position and to hold the means in fully opened position. I

Other objectives, features and advantages of the present invention will be readily apparent tothosev skilled in the art from the following detailed description of the drawings in which: I T

Figure lis' a diagrammatic view showing a typical ceiling installation of a blower incorporating the principles of the present invention in which air is: discharged through a duct which extends horizontally from a side of the blower casing. f

Figure 2 is a view similar to Figure lyin which the duct is shown leading vertically upwardly from the blower casing. I"

Figure 3 is a view of the underside of the blower casing in which certain parts have been broken away to illustrate details of construction. I 7

Figure 4 is a cross sectional view taken on the line 4-4 of Figure 3.

Figure 5 is a view similar to Figure 3 in which parts are broken away to illustrate the details of the means provided to secure the motor-blower unit in place; I

Figure 6 is a cross sectional view taken on the line 6-6 of Figure 5. In this view the parts are arranged for discharging air horizontally from a side of the blower casing.

Figure 7 is a view similar to Figure 6 in which the parts are arranged to discharge air upwardly vertically from the blower casing.

Figure 8 is a cross sectional view taken on the line 8-8 of Figure 4.

grill mounting Figure 9 is a enlarged cross sectional view taken on the line 9-9 of Figure 4.

For purposes of this disclosure, the blower, which is designated generally by the numeral 10, is shown installedin a ceiling. In Figure 1 it is shown between floors, for example, in a two story house. In an installation of this type, it is usually ncessary to run a duct, such as that shown fragmentarily only at 11, horizontally from a side of the blower in the spaces between joists to an exhaust outlet at the outside of the building structure. In an installation such as that shown in Figure 2, the duct 11 extends from the top of the casing. This type installation may be used in a one floor plan building structure, or in other places where conditions require. The two installations shown are intended to be representative only. It is believed that it will be obvious to those skilled in the art that the blower construction is adaptable to many other types of installations such as, by way of example only, an installation in an overhead storage cabinet of the type used in kitchens, an installation in a stove ventilator hood, an installation in a wall between studs, and an installation in the space provided by a dropped ceiling.

The blower is housed within a rectangular, sheet metal casing which is designated generally by the numeral 12. The casing, it will be noted, is square in lateral cross section. The casing includes two end walls which are '2,s42,ao7 I and are adapted to be engaged underneath of or through bands 30-30 which are lanced from the respective end walls 13 and 14 at the side thereof opposite side wall 16, or in the bands 31-31 which are lanced from the respective end walls at the edge thereof which is opposite to side wall 15. To change the transposable side wall 23 from one position to the other it may be disengaged from slots 27 and bands 39-39, for example, and reengaged in slots 28 and bands 31. In order to make the change, the end wall must be turned end for end. To fasten the transposable wall permanently in place the tabs 29 may be bent back around the bands, either those designated 30-30 or those designated 31-31 so as to lock the wall against removal from the casing. Preferably, the free edge of the transposable wall is beaded or ribbed as shown at 32 to strengthen it.

As will be seen from Figures 1 and 2 the casing 12 of the blower is dimensioned to tit between joists that indicated at 13 and 14 respectively and a side wall 15 which, in the present instance, are formed from one piece of sheet metal bent at right angles at the respective opposite ends of side wall 15. The three sided construction thus provided is permanently atlixed to another side wall which is designated 16. Three sides of wall 16 at the top and two ends thereof are flanged as at 17 to provide a means for attaching this wall to the three sided construction comprising end walls 13 and 14 and side wall 15. It is preferred that the flanges 17 be spot welded to walls 13, 14 and 15 so as to provide a rigid, four sided, self-sustaining structure. The wall 16 has two rectangular openings 18-18 therein adjacent to the edge thereof which joins side wall 15. These openings constitute the exhaust outlets for the blower and they open into a rectangular duct fitting or connector, designated 19, which is permanently afiixed in place. Right angular flanges 20 at three sides of the duct fitting are spot welded to wall 16 and .an extension 21 at the top of the duct, as viewed in Figure 8, overlaps the marginal edge of side wall 15 and is also spot welded in place. The lower edges of the two end walls 13 and 14, the lower edge of side wall 16, and the side edges of the respective end walls 13 and 14, as viewed in Figure 8, are configurated to provide strengthening ribs 22 which extend along these walls adjacentto their free edges.

The other two sides of the casing 12 are adapted to receive, interchangeably, either a transposable side wall 23 or a shiftable grill 24. It is the interchangeability of wall 23 with grill 24 which makes the present conare spaced on standard 16 inch centers. The respective end walls 13 and 14 of the casing are pierced as shown in Figures 1 and 2 to provide holes 33 for nails which may be used to fasten the casing to the joists, or to wall studding, or to support members in cabinet structure.

The grill 24 in the present embodiment is fabricated from a single piece of sheet metal. The grill includes a marginal frame 34, which may be substantially rectangular in shape with rounded corners, a plurality of grid members or bars 35 which extend longitudinally of the frame, and an upstanding peripheral flange 36 which is turned outwardly at its upper edge. As will be seen in Figure 6 the outwardly turned rim of flange 36 makes contact with the plaster surrounding the recess in which the blower is situated in a ceiling installation.

At the respective opposite ends of the grill, and on the longitudinal center line thereof, a pair of mount brackets 37 are secured by means of rivets to the inner face of frame 34. With the grill in place as shown in Figure 6 the respective mount brackets extend into the casing adjacent to the opposite end walls thereof. Each mount bracket has a pivot pin 38 secured therein which extends at right angles from a side thereof in axial alignment with the longitudinal center line of the grill. Each pin is rotatably engaged in an aperture which is provided in the end of a link designated 39. The other end of each link is pivoted upon means such as a rivet which is secured to the end wall in the corner thereof which is opposite to side walls 15 and 16. Furthermore, the point of pivot is on one of the diagonal lines of the end wall so that it is symmetrically placed with respect to the two sides of the casing which the shiftable grill is adapted to enclose. Substantially mid-way between the pivot pin 38 and the point at which the link is pivoted to the end wall a small hole 40 is provided in link 39,

struction adaptable to accommodate substantially all duct conditions likely to be found in ordinary building structures.

-Transposable side wall 23 has a flange 25 turned over at right angles at three edges thereof. The flanges are adapted to engage and embrace the outer marginal edges of the two end walls of the casing and the outer mar- 'ginal edge of a side wall. The flanged longitudinal side edge of the transposable wall 23 has three tabs thereon like the one shown at 26 in cross section in Figure 6. These tabs, although parallel to the plane of the flanged edge of transposable wall 23, are offset from it by one thickness of sheet metal, and are adapted to be engaged in complementary slots 27 which are provided along the edge of side wall, 15 or in slots 28 which are provided along the edge of wall 17. In addition, transposable wall 23 has a tab on each one of the flanges at theends thereof. The latter tabs are designated 29 which hole provides a means of attaching one end of an elongated coil spring 41. The other end of the coil spring may be secured to an angle bracket 42 or an angle bracket 43. These two brackets are substantially identical in construction and each may comprise a triangular metal plate which is flanged and spot welded to the fixed walls of the casing.

The means which are provided to mount the grill 24 performs several functions. The link permits the grill to be shifted from one side of the casing to the other side of the casing in order to change the direction and position of the duct fitting. The coil spring 41 in conjunction with the link 39 provides a toggle action which holds the grill tightly against the plaster line when it is in closed position, but, which in addition, serves to hold the grill links in open position when swung down as shown bythe dot-dash lines of Figure 6. In the latter position, it will be noted that the spring is moved over center with respect to the point of pivot for the link 39 so that the grill is stable when open.

' A comparison of Figures 6 and 7 will show how simple it is to change the relative position of the grill. In Fig ure -6 the grill is shown with the duct extending'from a side of the casing. To change it to the condition shown in Figure 7 all that it is necessary to dods to move the upper end of the coil spring 41 from bracket 42 overto bracket 43. This change, of course, can hemade without the use of special tools. At the same time, of course, the transposable wall 23 of the casing .is moved as described above.

The blower unit which is used to move the air-in the present construction comprises a pair of centrifugal type, squirrel cage blower wheels 44-44 which are keyed to the opposite ends of the shaft of a double ended electric motor 45. The blower wheels may follow conventional design, but it is preferred that theyare' made of steel in order that they maybe sufliciently rigid to keep them from becoming bent out'of line during cleaning.

The motor 45 is enclosed within a cylindrical jacket 46 which has a pair of blower housing cmounting rings 47-47 aflixed to its opposite ends. Volute housings 48-48 for the blower wheels are removably secured to the respective mounting rings 47-47 by means to be described below.

The motor and the blower wheels, the jacket for the motor and the two blower wheel housings comprise a structural unit which is adapted. to be readily removed from and replaced in the casing 12 through the grill side thereof as will be explained below.

As may be seen in Figure 9, the cylindrical jacket 46 for the motor is open at one side thereof to an air intake duct 49. This duct is made of sheet metal which is formed into a box-like structure open at both-ends. The duct 49 is permanently secured to. the jacket-46 by a pair of flanges 50 which are turned outwardly from the jacket and which are spot welded to :the duct. Duct 49 is located just below duct fitting 19 and is open to the outside of the casing through louvers 51 which are cut into the wall 16 of the blower casing. Cooling air is induced to flow into. jacket 4.6 through louvers 51 by the spinning blower wheels. The two wheels pull the air through a plurality of openings .52 in the mounting rings 47 which are secured to the opposite ends of the jacket. The louvers 51, it will be noted, open into the recess in which the casing is mounted so that the air used to cool the motor is not that which isdrawn through the grill. In this way, :an accumulation of greasy dirt in the jacket is avoided. Both ends ofijaclcet 46 are flanged as at 53, the flanges extending outwardly atright angles to the walls of the jacket. It is preferred that one of the flanges 53 be spot welded to :one of'the mounting rings. To facilitate assembly, the other flange is bolted to the other one of the two mounting rings.

' The mounting rings also serve to mount the motor 45.

The central area. of each ring 47 has. a circula-r opening therein in which is mounted a rubber grommet 54, the grommet having an annular groove extending around the circumference thereof which seats the marginal edge of the ring 47 in the area thereof immediately surrounding the opening. The end caps for the motor bearings may seat directly the respective. grommets. Eachmounting ring, in addition, has an annular, peripheral flange 55 thereon which is oflset inwardly ends of the motor jacket. It is these flanges which mount the yolute blower wheel housings. Each bIower wheel housing is secured to flange-47 by-rn'eans'of spring urged bayonet pin devices which are designated generally at 56*: Each device includes a pair of large headed pins 5757 and .a still .coil spring 58. The heads on the pins, it will he noted from Figure 4, taper outwardly as at 59 from the shank portion thereof. The two pins of each device. 56 are sliclab ly mounted in apertures in the respective annular flanges 47 47 opposite one another at points which :are aligned "parallel 'withthe motor axis.

The shanks of the heads; point toward one another and each has a transverse .hole thereth-rough which receives the hook end of spring 58;. Thespringis-underconsiden from the oppositeable tension, thus the heads of the two pins seat firmly against the apertures in the respective annular 'flanges,

In the instance shown, three bayonet pin devices 56 are employed, being located at substantially equally spaced points around the blower'jac'ket. Each volute housing 48 has three bayonet slots 60 in a wall thereof which are spaced in accordance with the locations of pins 57. Thus, to remove and replace the blower-wheel housings, each housing is twisted with 'respect to the motor jacket to align the large openings -in the bayonet slot with the heads of the pins. With the heads of the large openings lined up, the housing may be pulled straightolf the end of the blower wheel. I I

'The two blower wheel housings, other than having the bayonet slots in them, mayfoll'ow substantially conventional construction. In the presentinstance each housing comprisesan inner wall 61 having a circular opening 62-therein to seat upon a shoulder 63 which is provided where the annular flange 55 is turned outwardly from the mounting ring. The opposite or outer wall 64 of the blower housing has a large central opening 65 therein, the marginal edge of which may be turned in as at 66 to provide an air intake passageway which is-in com munication with the area inside of the blower wheel. Two side walls 61 and 64 areenclosed by a continuous wrap-around wall 67, the opposite side edges of which are flanged as at 68 to seat the peripheral edges of the respec-' tive side walls.

The motor blower unit isadapted to be fastened inside of the casing by means of a bail shaped latch indicated generally at '69. This latch'is pivoted at its opposite ends in brackets 7070 which may be spot welded or riveted to the opposite end walls of the casing. The pivotal axis of the bail shaped latch extends longitudinally of the casing in the quadrant thereof which is adjacent to the duct fitting; The bail shaped latch, when it is in blower unit locking position, extends from the pivot points at approximately 45 to the longitudinal axis of the casing to engage in detent grooves 71--71 which are formed by punching outwardly the metal of the around walls 67 of the two blower wheel housings. These -detents are located at places opposite the air outlets of the housings at approximately 45 to a plane passing vertically through the motor axis.

In the present construction, the whole blower casing is turned through toshiftfrom side discharge to yertical discharge. The blower motor unit is also turned in such movement inasmuch as the discharge openings from the blower wheel housing must remain aligned with the permanently aflixed duct fitting. With the duct fitting '19" extending from a side of the casing as viewed in Figure 9,- the bail shaped latch 69 may be swung up along the side of the blower motor unit which is opposite to the duct fitting to free the unit for removal through the opening provided by swinging the grill down into the position shown in Figure v6. With the discharge duet extending upwardly, the. bail bar' may be swung up to release the unit at mhe side thereof which is toward the duct fitting. In either instance, the swing is in the direction of the tnansposa'ble side wall 23 of the casing.

The electric motor 45- is powered through wiring 72 which passes through a. grommet 73 'seated in a hole in.

the motor jacket 46.- A male plug '74 is provided at the end of the wiring which plug is adapted to be engaged into a socket mounted within a wiring box- 75. Pref-- erably, the'wiring box is in one of the corners of the easing which is adjacent to a duct fitting. 'Thus located; it serves, with a nb76, to position the unit so that the open-' ings 1B-l 8 are aligned correctly with the blower wheel housings.

ILWill he noted :that' the :present blower unit is virtually free of vibration due to the fact that all mounting componerits are either fastened by springsor'held in place by spring members. The motor itself is seated within the respective wrap-- are secured by the spring urged bayonet pin devices 56 and bail latch 69 employed to secure the motor blower unit in place also has a certain amount of sprin'giness, and inaddition; the grill is held in place bythe springs 41-41. For the initial shipment of the blower, the transposable side wall may be taped or otherwise temporarily affixed to oneof the sides of the casing. At the point of installation the transposable wall and shiftable grill may ,be arranged as conditions dictate. Then, with the motorblower unit out, the casing may be fastened into place by nails or screws which pass through the holes provided in the two end walls. In an installation in a new building structure, the casing may be put in place before plastering so that the plaster line may come right up to the casing walls, In an installation in an old building, if care is exercised in' cutting the hole through the plaster, it is not necessary to plaster in the areas immediately surrounding the casing, because the substantially wide frame on the grill will hide the broken edges of the old plaster.

To clean the unit the grill may be swung down into open position, and then disengaged from the links which remain in down position due to the toggle action provided by the springs 4141. The bail then may be disengaged and the motor-blower unit removed from the casing. Any dust or dirt'at the inside of the casing then may be cleaned out. The blower wheel housings may be removed from the motor jacket by turning to release the bayonet pins. The housings, after removal, may be washed in the sink, if desired. The blower wheels may be brushed to remove any accumulation of dust or dirt from the blades. It is preferred that appropriate markings be made on the two blower wheel housings and on the motor jacket to serve as a guide to assist in the reassembling of the motor-blower unit so that the housings are correctly related to one another and to the motor. With the motor-blower unit assembled it may be re-installed in the casing by swinging the bail latch to one side and then re-engaging it in the detents once the unit is properly seated.

Having described my invention I claim:

1. A motor-blower unit for installation in a recessed casing, said motor-blower unit comprising an electric motor having a drive shaft extending axially from each of its opposite ends, a rigid cylindrical jacket substantially enclosing said motor, a pair of mounting rings secured to the opposite ends of said cylindrical jacket, resilient means mounting the opposite ends of said motor insaid mounting rings, a pair of blower wheels, each wheel of the pair secured to a shaft at an end of said motor, a pair of volute blower wheel housings, said rings configurated to seat said housings and means to removably secure said volute blower wheel housings to the respective mounting rings at the opposite ends of said cylindrical jacket.

2. A motor blower unit as set forth in claim 1 in which at least one of the mounting rings has a plurality of apertures therein opening from the adjacent blower wheel housing to the motor inside the jacket, and means to admit air into the jacket from a side thereof, whereby the blower wheel in said adjacent housing, when in operation, pulls air over the motor to cool the same.

3. A motor blower unit as set forth in claim 1 in which the volute blower wheel housings are configurated to receive means for removably securing the unit in said casing, whereby the resilient means mounting the opposite ends of the motor, in insulating the vibrations of the motor, prevent transmission of these vibrations to the mounting rings, through the blower wheel housings and thence to the casing.

4. In a blower having a rectangular casing with a duct fitting associated with one of the side walls thereof, a motor blower unit including a pair of blower wheel housings and means to removably mount said unit in said casing to exhaust through said duct fitting, said means comprising a' substantially U-shaped bail, said bail having a substantially horizontally disposed latch portion and two arms extending-in the same plane from opposite ends of said latch portion, means to pivotally mount the outer ends of the arms of the bail on opposite side walls of, the casing, and means on the blower wheel housings engageable 'with the horizontal latch portion of said bail.

:'5.'A motor-blower unit adapted to be installed in a recessed casing, said motor-blower unit comprising an electric motor having a shaft projecting from each end thereof, a squirrel cage blower wheel mounted upon the shaft at each end of said motor, a rigid jacket substantially enclosing said motor, a pair of mounting rings affixed to the respective opposite ends of said jacket, means to resiliently mount the opposite ends of said motor in the respective mounting rings, an annular, peripheral flange on each of said mounting rings, a pair of volute blower wheel housings, means to seat each blower wheel housing of the pair upon the respective mounting rings against said flange in a position to enclose a blower wheel, and bayonet pin means removably fastening said blower wheel housings to the respective annular flanges of the mounting rings.

6. A motor-blower unit adapted to be removably installed in a casing, said motor-blower unit comprising an electric motor having a drive shaft extending axially from each of' its opposite ends, a rigid cylindrical jacket substantially enclosing said motor, a pair of circular mounting plates secured to the opposite ends of said cylindrical jacket, resilient means mounting the opposite ends of said motor in said mounting plates, a pair of blower wheels, each blower wheel of the pair secured to the motor shaft at an end of the motor immediately to the outside of a mounting plate, a pair of volute blower wheel housings, each volute housing having a circular opening at the inner side thereof which is larger in diameter than a blower wheel so as to fit over it, a plurality of bayonet pin slots disposed around the circular opening in each volute blower housing, a plurality of bayonet pins slidably mounted in each circular mounting plate and having heads thereon engageable in said slots, said pins disposed in pairs opposite to one another in the respective plates and each pair being interconnected by a coil spring to removably hold the blower housings against the circular plates under spring tension, whereby the volute blower housings may be removed by disengaging said pins from said slots in order that the housings may be cleaned and in order that the blower wheels may be exposed for cleaning.

7. A motor-blower unit adapted to be removably installed in a casing, said motor-blower unit comprising an electric motor having a drive shaft extending axially from each of its opposite ends, a rigid cylindrical jacket substantially surrounding said motor, a pair of circular mounting plates secured to opposite ends of the cylindrical jacket, resilient means mounting the opposite ends of said motor in said mounting plates, a pair of blower wheels, each wheel of the pair secured to the motor shaft at an end of the motor immediately to the outside of a mounting plate, said mounting plates each having an annular seat thereon which is larger in diameter than the blower wheels, a pair of volute blower wheel housings, each housing having a circular opening at its inner side which is engageable with an annular seat on a mountmg plate, and means removably securing the blower wheel housings to the respective circular plates, the last named means permitting the blower wheel housings to be removed from the plates in order that they may be cleaned and to expose the blower wheels in order that they may be cleaned.

8. .A motor-blower unit adapted to be removably installed in a casing, said motor-blower unit comprising an electric motor having a drive shaft extending axially from eachiof its opposite. ends, a rigid cylindrical jacket substantially enclosing said motor, a pair of circular mounting plates rigidly secured to the opposite ends of said cylindrical jacket, resilient means mounting the opposite ends of said motor in said circular mounting plates, a pair of blower wheels, each wheel of the pair secured to the motor shaft at an end of the motor immediately to the outside of a mounting plate, the mounting plates being substantially larger in diameter than the blower wheels, a pair of volute blower wheel housings, each housing having an air intake opening at the outer side thereof, the inner side of said volute housing having a circular opening therein is larger in diameter than a blower wheel, but smaller in diameter than a circular plate, and means removably securing the blower wheel housings to the respective circular mounting plates to enclose said wheels, the last named means and the circular openings at the inner sides of the housings permitting said housings to be removed from the unit in order that the housings may be cleaned and to expose the blower wheels in order that they may be cleaned.

Marker et a1. May 23, 1944 Marker June 14, 1955 

